Voltage-limiting device



Feb. 16 1926. 1,573,068

R. K. HONAMAN VOLTAGE LIMITING DEVICE Filed April 6, 1922 Patented Feb. 16, 1926.

TnLnrI-oNE AND TELEGRAPH COMPANY, A

K. non-AMAN, or enoo'nrrnnn, New JERSEY, AssiGNon To' AMERICAN conronAT'roN or 'New' YORK.

VOLTAGE-LMITNG DEVICE.

Application filed April 6,

To all 'io/tom t may concern.'

lle it 1xnown that l, Bici-nino l'. HoNxMAN, residing at Bloomfield, in the county ot '.llsscx and State ot New Jersey, have invented certain improvements in Voltageiiin'iiting Devices, oi which the 'following is a specilication.

'l his invention relates to voltage limiting devices and particularly to a type ci multiwindingl transformer which is designed to limit the magnitude of the potential that may be applied to a selected section otl a circuit.

lrn the operation ot telephone circuits, such tor example as long circuits, which are exposed to inductive interference by neighboring power circuits operated at relatively hig-h potentials, trouble known as cacoustic shock77 is experienced particularly by the telephone operators when a high potential surge is set up in the exposed circuit, due, for example, to the accidental grounding of the power circuit. The abnormal potential induced in the telephone line circuit produces an abnormal click in the telephone head receiver' ot' the operator. The result ot such acoustic shock interferes with the normal operating routine and therefore is detrimental to the service.

lt is the object ot this invention to provid-e means tor limiting the potential that may ne impressed by an exposed line circuit upon the operators telephone circuit so that the current in the operators receiver can never' exceed a predetermined value regardless ot the potential applied across the line circuit, thereby preventing what is known as acoustic shock.

'This inventionwill be better understood trom the following description when read in connection with the attached drawing', which shows one form oit embodiment ot the invention.

l ln the drawing, l represents a telephone `lino circuit which is exposed to inductive interference from the adjacent power circuit '2. The line circuit l is connect-ed by means ot the transtori'ner 8 with the switchboard circuit 4, which has connected thereto an operatofs telephone set 5. Although the circuit 4l has been referred to as a switchboard circuit it is to be understood that this may be any circuit as, tor example, the circuit extending to a subscriber. 4Since the eli'ect ot acoustic shock is usually most 1:?22. Serial No. 550,072.

severe in the operators telephone sets, the invention has therefore been described in connect-ion with a switchboard circuit and the operatorie telephone set.

lridged across the sides ot the line circuit l is a .spark gap arrester (i, which may be ot any well-known type, having electrodes 7 connected with the sides ot the line and a grounded plate 8 inserted between the electrodes but not in contact therewith. 9 represents signaling apparatusof any well known type that may be connected across a line circuit such as l. Y

The transformer 3 comprises a plurality ot windings7 the main windings l0 and ll being connected with the line circuit l and the switchboard circuit 4 respectively. These windings have preferably the same number otl turns so as to eliect unity ratio ot transformation between the line. circuit and the switchboard circuit. rlhe line winding lt) has connected in series therewith a condenser lS, in accordance with standard telephone practice lor certain tvpes ot trunks, but this may be omitted without impairing the scope ot this invention. Inductively connected with the windings l0 and ll is anauxiliary winding l2 having a greater number o t turns than the main windings lO and ll. rThis winding has Vin series therewith a spark gap protector let which may be adjusted to operate at any given potential. The ratio ot transformation of the winding l2 to winding l0 .should preferably be quite large. These windings are all arranged upon the same core, which is preterably ot' a toroidal type such as is used in telephone repeating coils. The switchboard circuit 4 has connected in series with the sides thereof condensers 15 and 16, which is in accordance with .standard practice Jtor certain types of trunks.

Having in mind the foregoing description ot the circuit in which this invention is embodied it will be better understood 'trom the following description of the mode ot operation ot the circuit. Then a signaling potential such, tor example, as that used by voice frequency waves, is impressed across the distant end ot the line l, the cur-rent resulting there/trom flowing through the winding l() ot the transformer 3 will induce a potential difference in the winding ll which will cause current o't normal magnitude to liow through the receiver ot the operators telephone set 5, connected with the switchboard circuit 4. A voltage will also be induced in the winding 12 of the transformer which will be of greater magnitude than that which is induced in the winding 11, since the ratio of transformation is greater between windings 10 and 12 than between windings 10 and 11. This voltage, however, will not be suiliciently great to are across the air gap of the protector 14, and consequently the ciicuit of the winding 12 will remain open. It will therefore be seen that under conditions of normal operation the impedance across the winding 12 will be high and the windings 10 and 11 will function in the same manner as in the present type of telephone repeating coil. Under these conditions the transmission characteristics of the coil will be about the same as those of the present standard type of coil. If, during the course of transmission of voice signals over-the line circuit 1, or during any time in which the operator-s telephone set is connected with the line 1, the power circuit induces a high potential across the conductors of the line circuit 1, this abnormal potential will ordinarily be applied to the operators telephone set and produce severe acoustic shock. Since, however, in the applicants arrangement there is inductively connected to the line winding 10 an auxiliary winding 12, which is adapted to step up the voltage impressed thereon, this abnormal high potentialwill induce a greater potential in the winding 12, which will cause the air gap vof the protector 1t to break down at a predetermined voltage. This, therefore, affords a low impedance path into which most of the energy resulting from the inducedhigh potential will flow, and thereby the switchboard circuit Ll and its associated apparatus is protected. In most instances the amount of energy which would be transferred across the air gap of the protector 14 would be small so that it would be unnecessary to renew the protector except atl infrequent intervals.

Although this invention has been disclosed as embodied in a particular circuit arrangement itis to be understood that it is capable of embodiment in other forms and arrangements without departing from the spirit and scopek of the appended claims.

lVhat is claimed is: 1. In a signaling-system, the combination with a line circuit inductively exposed to a power circuit capable of inducing abnormal potentials in the said line circuit, of a switchboard circuit, and a transformer having main windings connected with and adapted to inductively relate said line circuit to said switchboard circuit, and having an auxiliary winding in series with a spark gap adapted to operate at a definite potential in said auxiliary winding.

2. In a signaling system, the combination with a line circuit exposed to inductive interferenee of ay switchboard circuit and a transformer having main windings individual to and connected with said line circuit and said switchboard circuit, and adapted to inductively relate the said circuits, aiid an auxiliary winding inductively related to said main windings and having :l spark gap across the terminals of the said auxiliary winding adapted to operate at a definite potential in the said winding.

3. In an acoustic shock pieventioii device, the combination of a multiwinding transformer having main windings of subst-antially equal ratio, and a tertiary winding having a greater number of turns than the said main windings, a line circuit exposed to inductive interference connected with one of said main windings, a telephone circuit connected with the other of said main windings and a spark gap connected in series with said tertiary winding and adapted to become conductive when the potential in the said winding reaches a predetermined value.

1l. In a system for protecting against high potentials, the combination with an exposed circuit adapted to have a potential set up therein by an extraneous source, of a circuit to be protected, and a transt'oinler having main windings individual to and connected. with the said exposed circuit and the said circuit to be protected and adapted to inductively connect the said circuits, and an auxiliary winding induetively related to the said main windings and having a spark gap across the terminals of the said auxiliary winding to operate at a definite potential in the said winding.

5. In a system for protecting against high potentials, a combination with a multiwinding transformer having a plurality of main windings and a tertiary winding, a line circuit exposed to inductive interference connected with one of said main windings, a circuit to be protected connected with the other of said main windings and a spark gap connected in series with the said tertiaryY windingl and adapted to become conductive when the potential in the said windingI reaches a predetermined value. i'

In testimony whereof, I have signed niv naine to this specification this 5th day of April 1922.

RICHARD K. HONAMAN. 

